This invention relates to tube bases and more particularly to tube bases for cathode ray tubes which employ high voltage differentials between various tube pins.
Current and projected types of cathode ray tubes, particularly those employed in color television, have a small diameter neck containing the electron gun or guns. The necessary operating voltages for the various elements of these guns (heaters, cathodes, grids, focusing electrodes, etc.) are supplied via tube pins which are sealed into the end of the tube. As higher voltage guns have developed and the neck diameter has gotten smaller, decreasing from 36 mm to 29 mm, it has dictated that the tube pins, which are annularly arrayed thereabout, keep getting closer together.
Prior art tubes have always had large voltage differentials, sometimes on the order of 5 KV to 8 KV between various tube pins. Furthermore, if an arc originates between the anode and focus grid, the focus grid momentarily assumes anode potential (up to 30 KV) and this voltage can progress to the tube pins resulting in arcing from the focus pin to an adjacent pin, often damaging cathode emission. This subsequent arcing often occurs in the restricted area between the plastic base and the glass stem of the cathode ray tube. The intense heat developed by the arc results in a condition called "tracking"; a breakdown of the plastic base into a carbonaceous residue between the arcing pins, which results in a subsequent low insulation resistance.
Previously, it was attempted to control this arcing by surrounding a high voltage tube pin with an RTV; i.e., a room temperature vulcanizing silicone rubber. However, this process is difficult to control and required a trained operator. Additionally these high voltage connections have usually had some form of arc protection incorporated into the female socket, see, for example, U.S. Pat. Nos. 3,466,491 and 3,466,492. Such protection however, has proven incapable of providing adequate protection for the newer tube types.